1. Field of the Invention
The invention relates to a power supply device and more particularly to a parallel power system without an ORing device at output terminals thereof.
2. Description of the Related Art
Many modern devices and systems need backup power, a power supply with multiple power sources, or a power supply system capable of choosing a power source. If a device needs multiple power sources, there are some problems associated with combining power sources, choosing a power source, protecting a bus connected to power sources, and so on. If a parallel power system doesn't have a protective device, a system will break down during operation or operate abnormally due to failure of one power source or multiple power sources in the system. Generally, in a power system with multiple power sources in parallel, an ORing device is connected to output terminals of power sources so as to isolate power sources from supply lines.
Nevertheless, if there's no ORing device at output terminals of power sources of a power system, when power sources are connected in parallel and an output of the power system is abnormal due to failure of a DC-to-DC converter of one of power sources or other units in the circuit, the power system can't determine which one of the power sources has failed just by monitoring power sources. That is, because output voltages of DC-to-DC converters of power sources are coupled to a voltage of a bus. In this situation, if a power source which doesn't have a failure is turned off, the power system will result in a power failure and operate abnormally.